Device for evaluating tire rolling resistance

ABSTRACT

A device for evaluating tire rolling resistance, the device includes: load rolls having surfaces that simulate a road surface on which a tire is to travel; a moving mechanism; a load sensor; a position sensor; a phase difference calculation unit; and a rolling resistance evaluation unit. The load rolls are two or more load rolls disposed side by side and are smaller in diameter than the tire.

TECHNICAL FIELD

The present invention relates to a device for evaluating tire rollingresistance.

BACKGROUND ART

One of important measurement items in measurement of properties andperformance of a tire of a truck, a car, or some other vehicle is therolling resistance of the tire.

The rolling resistance of a tire is a force in the tangential directionthat occurs between the tire and a ground when the tire is rolled on theground. In a tire testing machine, the rolling resistance of a test tireis measured as a force in the tangential direction that occurs betweenthe tire and a counterpart surface (e.g., the surface of a load drum)that rotates being in contact with the tire. That is, when a radialforce (load Fz) having a certain magnitude is applied between the tireand the counterpart surface, a rolling resistance Fx corresponding tothe load Fz occurs. In this manner, a relationship between the load Fzand the rolling resistance Fx is measured.

Such a rolling resistance measuring method is prescribed in JIS D 4234(Method for measuring the rolling resistance of tires for cars, trucks,and buses, 2009) as a method using a drum tire running testing machine.

For example, an instrument disclosed in Patent Document 1 is known as arolling resistance testing machine that conforms to the JIS standard.The rolling resistance measuring instrument disclosed in Patent Document1 is configured in such a manner that a tire is brought into contactwith, that is, pressed against, the outer circumferential surface of acylindrical load drum (i.e., running drum) and a force and torque(moment) acting in each of the x, y, and z directions is measured by amulti-component force detector for a spindle that supports the tire viaa bearing. This instrument of Patent Document 1 is configured so as tomeasure a relationship between the axial load Fz on the tire and therolling resistance Fx with a correction on interference between thecomponent forces.

However, it takes a very long time for the rolling resistance measuringinstrument of Patent Document 1 to measure rolling resistances of alltires manufactured because it takes considerable time to measure arolling resistance of one tire.

To reduce the time to measure a rolling resistance of a tire, PatentDocument 2 discloses a technique for predicting a rolling resistancecoefficient using a tire uniformity tester for testing the uniformity ofa tire. It is known that the rolling resistance occurs due to energyloss that is caused by deformation of a tire rubber member duringrolling of the tire and is highly correlated with the attenuationproperty of the tire rubber member. In view of this, in Patent Document2, a method for predicting a rolling resistance coefficient by measuringan attenuation property that appears as a phase difference between thedrum displacement and the reaction force while exciting the tire using adrum that is provided in the tire uniformity tester was devised. Thismethod is characterized in that a phase difference corresponding to anattenuation property of each tire is measured in a uniformity measuringprocess for testing all tires and abnormal tires are sorted out whoserolling resistance coefficient values are out of a standard range. Tosort out abnormal tires, a phase of a reference tire whose rollingresistance coefficient is within the reference range is calculated inadvance by the method of Patent Document 2. A measured phase of a tiremanufactured is compared with the phase of the reference tire and thetire manufactured is judged defective if the difference is larger thanan allowable value.

CITATION LIST Patent Literature

Patent Document 1: JP-A-2003-4598

Patent Document 2: JP-A-2015-232545

SUMMARY OF INVENTION Technical Problem

However, in the method of Patent document 2 in which a tire is excitedusing a load drum, when the load drum has a large mass (i.e., when aload drum whose diameter is larger than a tire diameter is usedconventionally in order to make tire deformation closer to that as wouldoccur on a flat surface), it is necessary to increase the capacity ofits motive power source in order to obtain a prescribed excitationamplitude. Furthermore, there are problems relating to fatigue damage ofthe members constituting the drum and vibration and fatigue of theentire device.

The present invention has been made to solve the above problems, and anobject of the invention is to provide a device for evaluating tirerolling resistance in which the capacity of an air cylinder that is amotive power source for obtaining an excitation amplitude for a loaddrum can be decreased and vibration and fatigue damage of the entiredevice and the members constituting the drum can be reduced.

Solution to Problem

A device for evaluating tire rolling resistance according to theinvention includes load rolls having surfaces that simulate a roadsurface on which a tire is to travel; a moving mechanism configured tomove the load rolls alternately in an approaching direction in which theload rolls come closer to the tire and in a leaving direction in whichthe load rolls go away from the tire; a load sensor configured to detecta load acting on the tire in a state where the surfaces of the loadrolls are in contact with the tire; a position sensor configured todetect a position of the load roll in a direction along the approachingdirection and the leaving direction; a phase difference calculation unitconfigured to control the moving mechanism so that the load acting onthe tire is varied and calculates a phase difference between a variationof the load and a variation of the position of the load rolls on thebasis of signals from the load sensor and the position sensor; and arolling resistance evaluation unit configured to evaluate a rollingresistance of the tire as an evaluation target by comparing the phasedifference calculated for the evaluation target tire by the phasedifference calculation unit with a phase difference calculated for areference tire by the phase difference calculation unit. The load rollsare two or more load rolls disposed side by side and are smaller indiameter than the tire.

According to the embodiment, because of the use of the load rolls thatare smaller in diameter than the tire, the mass of the load rolls can besignificantly reduced. This makes it possible to decrease the capacityof a motive power source for obtaining a prescribed excitation amplitudefor the load rolls and to reduce vibration and fatigue damage of theentire device and the moving mechanism. By disposing the two or moreload rolls side by side, the contact state of the tire can be madecloser to its actual ground contact state and the curvature ofdeformation of the tire can be made smaller.

It is preferable that the load rolls be disposed separately from a tiretesting machine for testing the tire. Since the load rolls are disposedseparately from the tire testing machine, a device for evaluating tirerolling resistance having the same specification can be installed easilyin various testing machines of different manufacturers or differenttypes without modifying existing test machines or subjecting them toonly simple modifications.

It is preferable that the load rolls be disposed separately from arunning drum of the tire testing machine, With this measure, a devicefor evaluating tire rolling resistance can be installed withoutmodifying an existing tire test machine, in particular, a tireuniformity tester, or subjecting an existing tire test machine, inparticular, a tire uniformity tester, to only simple modifications.

It is preferable that the load rolls be two load rolls and the centersof the respective load rolls be located between two straight lines thatare tangential to the tire and pass through the center of an imaginarycircle that is tangential to the tire and has the same diameter as theouter diameter of the tire.

As the dimension of the two load rolls in the radial direction becomeslarger, the distance between the centers of the two load rolls increasesand the contact states of the load rolls and the tire become muchdifferent from an actual ground contact state of the tire. In view ofthis, by locating the centers of the load rolls between two straightlines that are tangential to the tire and pass through the center of animaginary circle that is tangential to the tire and has the samediameter as the outer diameter of the tire, the distance between thecenters of the two load rolls can be made small and the contact state ofthe tire can be made closer to its actual ground contact state.

The device for evaluating tire rolling resistance may be such that themoving mechanism has an air cylinder and the load rolls are configuredto apply exciting force to the tire by switching the pressure suppliedto the air cylinder between high pressure and low pressure.

Since the moving mechanism has an air cylinder, an inexpensive andsimple motive power source can be provided. Switching the pressuresupplied to the air cylinder between high pressure and low pressureallows the load rolls to apply stable exciting force to the tire.

Advantageous Effects of Invention

According to the embodiment, because of the use of the load rolls thatare smaller in diameter than the tire, the mass of the load rolls can bereduced to a large extent. This makes it possible to decrease thecapacity of a motive power source for obtaining a prescribed excitationamplitude for the load rolls and to reduce vibration and fatigue damageof the entire device and the moving mechanism. By disposing the two ormore load rolls side by side, the contact state of the tire can be madecloser to its actual ground contact state and the curvature ofdeformation of the tire can be made smaller.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a device for evaluating tire rollingresistance according to an embodiment of the present invention and atire uniformity tester.

FIG. 2 is a sectional view of the device for evaluating tire rollingresistance viewed from the side.

FIG. 3 is a plan view of the device for evaluating tire rollingresistance.

FIG. 4 is a front view of the device for evaluating tire rollingresistance.

FIG. 5 is an air circuit diagram for driving an air cylinder.

FIG. 6 is a plan sectional view of load rolls and a tire illustrating arelationship between the load rolls and the tire.

FIG. 7 is a plan sectional view of the load rolls and the tireillustrating a state where the load rolls are pressed against the tire.

FIG. 8 is a block diagram illustrating an electrical configuration ofthe device for evaluating tire rolling resistance.

FIG. 9 is a graph schematically illustrating a phase difference betweenthe displacement of load rolls and the load amplitude.

FIG. 10 is a side view of a device for evaluating tire rollingresistance that is applied to a tire having a small outer diameter.

FIG. 11 is a side view of the device for evaluating tire rollingresistance that is applied to a tire having a large outer diameter.

FIG. 12 is a side view of a device for evaluating tire rollingresistance according to a first modification.

FIG. 13 is a front view of the device for evaluating tire rollingresistance according to the first modification.

FIG. 14 is a side view of a device for evaluating tire rollingresistance according to a second modification that is applied to a tirehaving a small outer diameter.

FIG. 15 is a side view of the device for evaluating tire rollingresistance according to the second modification that is applied to atire having a large outer diameter.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are hereinafter described withreference to the accompanying drawings.

As shown in FIG. 1, a device for evaluating rolling resistance 10(hereinafter referred to simply as an “evaluation device”) according tothis embodiment is installed in a tire uniformity tester (TUM) 1 forperforming a tire uniformity test (JIS D 4233) in which the uniformityof a tire 2 in the circumferential direction is tested. Since theevaluation device 10 is installed separately from, rather thanintegrated with, the tire uniformity tester 1, a load roll 44 (i.e., 44Aand 44B) is disposed separately from a running drum 4 of the tireuniformity tester 1. The evaluation device 10 is installed on theopposite side of the tire 2 to the tire uniformity tester 1. The tire 2is annular shaped and is rotatably supported by a tire shaft 3 thatextends in the vertical direction. There are no particular limitationson the place at which the evaluation device 10 is installed except thatthe evaluation device 10 should be installed at such a place as not tointerfere with the tire uniformity tester 1, in particular, its runningdrum 4.

The evaluation device 10 evaluates a rolling resistance of the tire 2 bybringing, into contact with the tire 2, the load roll 44 (see FIG. 2)having a surface (i.e., outer circumferential surface) that simulates aroad surface on which a tire is to travel. The evaluation device 10 isfixed to a fixing member 6 that is installed on a base 5 so as to extendin the vertical direction.

The evaluation device 10 is equipped with an erected wall 11 fixed tothe fixing member 6 so as to extend in the vertical direction (i.e.,top-bottom direction in FIG. 2), a base frame 26 extending in ahorizontal direction (i.e., left-right direction in FIG. 2) that isperpendicular to the erected wall 11, and a housing 30 configured to bemoved in the horizontal direction on the base frame 26.

Also referring to FIG. 3, an air cylinder 13 that has a tip portionconnected to a projected wall portion 35 of the housing 30 and therebyconnects the erected wall 11 and the projected wall portion 35 of thehousing 30 is fixed to the housing 30 side of the erected wall 11. It isdesirable that the air cylinder 13 be disposed at such a position thatthe load rolls 44 can apply loads to the tire 2 at positions close toits center line. The air cylinder 13 is disposed at a position close tocentral portions of the load rolls 44 in the height direction andconstitutes a moving mechanism.

The moving mechanism (i.e., air cylinder 13) moves, alternately, via thehousing 30, the load rolls 44 in an approaching direction in which theload rolls 44 come closer to the tire 2 (rightward in FIG. 3) and in aleaving direction in which the load rolls 44 go away from the tire 2.(leftward in FIG. 3). The air cylinder 13 has a housing-30-side pressurechamber 15 that is defined by a piston 14, and moves the housing 30 bymeans of a piston rod 16 through switching of the pressure in thepressure chamber 15. Two springs 12 connecting the erected wall 11 and aback wall 34 of the housing 30 are disposed on the housing 30 side ofthe erected wall 11 so as to accompany the air cylinder 13. The twosprings 12 urge the housing 30 toward the erected wall 11 withoutobstructing the movement of the load rolls 44 caused by the air cylinder13.

FIG. 5 shows an air circuit 20 for driving the air cylinder 13. Thepressure in the pressure chamber 15 of the air cylinder 13 is switchedby the air circuit 20 that is connected to a pressure source 21. The aircircuit 20 consists of a high-pressure-side high-pressure regulator 22and a low-pressure-side low-pressure regulator 23 that are connected inparallel between the pressure source 21 and a second electromagneticvalve 25 that is connected to the air cylinder 13. A firstelectromagnetic valve 24 is connected between the high-pressureregulator 22 and the second electromagnetic valve 25. Switching thefirst electromagnetic valve 24 from off to on establishes a state wherehigh-pressure air or low-pressure air can be supplied to the pressurechamber 15 of the air cylinder 13.

High-pressure air is supplied to the pressure chamber 15 by turning offthe second electromagnetic valve 25 in a state where the firstelectromagnetic valve 24 is on. Low-pressure air is supplied to thepressure chamber 15 by turning on the second electromagnetic valve 25 ina state where the first electromagnetic valve 24 is on. If the firstelectromagnetic valve 24 and the second electromagnetic valve 25 areswitched from on to off, supply of air to the pressure chamber 15 isstopped and the pressure in the pressure chamber 15 becomes atmosphericpressure.

Returning to FIG. 2, rails 28 of a pair of linear guides 27 extendingstraightly on the base frame 26 from the end on the erected wall 11 sideto the end on the tire 2 side (i.e., the right-hand end in FIG. 2) arefixed to the top surface of the base frame 26.

The housing 30 supports the load roll 44 rotatably and reciprocates theload roll 44 against the tire 2 at constant vibration frequency alongthe linear guides 27. As seen by also referring to FIG. 4, the housing30 has a vertically long box shape that is open on the front side (i.e.,viewer's side in FIG. 4) and is equipped with a bottom wall 31, a topwall 32, side walls 33, a back wall 34 (see FIG. 3), and the projectedwall portion 35.

The bottom surface of the bottom wall 31 is provided with sliders 29that slide along the rails 28 of the linear guides 27. Attached to thebase frame 26 via the linear guides 27, the housing 30 (i.e., load rolls44) can be prevented from tilting. A variation amount of the housing 30moving alongside the linear guides 27 is measured by a position sensor37 fixed to the erected wall 11. In other words, by detecting avariation amount of the housing 30, the position sensor 37 detects aposition of the load rolls 44 in a direction along the direction inwhich the load rolls 44 conic closer to the tire 2 and the direction inwhich the load rolls 44 go away from the tire 2. Although in theembodiment a non-contact laser displacement meter is used as theposition sensor 37, the position sensor 37 may be a contact displacementmeter or a non-contact eddy current displacement meter.

Load cells 38 that are load sensors for detecting a load acting on thetire 2 in a state where the surfaces of the load rolls 44 are in contactwith the tire 2 are installed on the bottom surface of the bottom wall31 and the top surface of the top wall 32, respectively. Top roll fixingmembers 42 fixing the top ends of two roll shafts 41 are attached to theupper load cell 38, and bottom roll fixing members 42 fixing the bottomends of the two roll shafts 41 are attached to the lower load cell 38.Each of the two roll shafts 41 supports the associated load roll 44rotatably via bearings 43. With the above configuration, when the loadrolls 44 are pressed against the tread surface of the tire 2, loads aretransmitted to the load cells 38 via the roll shafts 41 and the rollfixing members 42 and the load acting on the tire 2 is measured by theload cells 38. Since all of the loads acting on two load rolls 44 (44A,44B) act on the load cells 38, the load can be measured accurately.

The load rolls 44 are cylindrical members whose axes extend in thevertical direction, and the outer circumferential surfaces of the loadrolls 44 serve as simulated load surfaces for tire testing. FIG. 6 is aplan sectional view of the load rolls 44 and the tire 2 illustrating arelationship between the load rolls 44 and the tire 2 in a state wherethe load rolls 44 are in contact with the tire 2. The two load rolls 44Aand 449 are disposed side by side and each of the load rolls 44A and 44Bis smaller in outer diameter than the tire 2. A minimum value of theouter diameter of each load roll 44 is determined by its strengthagainst a load. In the embodiment, the ratio between the diameter of thetire 2 and that of the load rolls 44A and 44B is 5:1. The two load rolls44A and 44B have the same external dimension (i.e., same shape) andthere are no particular limitations on specific numerical value of theouter diameter of the load rolls 44.

In the two load rolls 44, the distance L3 between the center C2 of theone load roll 44A and the center C1 of the tire 2 is equal to thedistance L4 between the center C3 of the other load roll 44B and thecenter C1 of the tire 2. That is, the center C2 of the one load roll 44Aand the center C3 of the other load roll 44B are located on a circlethat is concentric with the tire 2. The center C5 of a line L5 thatconnects the center C2 of the one load roll 44A and the center C3 of theother load roll 44B is located on a line L6 that connects the center C1of the tire 2 and the center C4 of an imaginary circle 46 (describedlater).

Furthermore, the center C2 of the one load roll 44A and the center C3 ofthe other load roll 44B are set so as to be located between two straightlines L7 that are tangential to the tire 2 and pass through the centerC4 of the imaginary circle 46 that is tangential to the tire 2 and hasthe same diameter as the tire 2. The two load rolls 44A and 44B aredisposed in such a manner that their outer circumferential surfaces areseparated from each other.

The evaluation device 10 is further equipped with a phase differencecalculation unit 48 and a rolling resistance evaluation unit 49. Asshown in FIG. 8, the aforementioned moving mechanism of the air cylinder13, the position sensor 37 and the load cells 38 are connected to thephase difference calculation unit 48 and the phase differencecalculation unit 48 is connected to the rolling resistance evaluationunit 49. The phase difference calculation unit 48 controls the aircylinder 13 so as to vary the load acting on the tire 2 and calculates aphase difference between a load variation and a variation of the surfaceposition of the load roll 44 on the basis of signals from the positionsensor 37 and the load cells 38. The rolling resistance evaluation unit49 evaluates a rolling resistance of the tire 2 as an evaluation targetby comparing the phase difference calculated for the tire 2 as theevaluation target by the phase difference calculation unit 48 with aphase difference that was calculated for a reference tire by the phasedifference calculation unit 48.

Next, an evaluation method of a rolling resistance of the tire 2 usingthe evaluation device 10 according to the embodiment is described. Arolling resistance evaluation test is conducted after moving the runningdrum 4 away from the tire 2 after a tire uniformity test that wasperformed using the running drum 4.

In the evaluation device 10 according to the invention, the tire 2 isevaluated using a parameter tan δ that represents an attenuationproperty of a tire rubber. For example, resistance due to energy loss(i.e., hysteresis loss) that is caused by repeated deformation of a tirerubber deformed by a load due to its rotation is a major factor ingeneration of a tire rolling resistance. This hysteresis loss can beevaluated using tan δ. Parameter δ of tan δ corresponds to a phasedifference between stress and deformation generated when a periodicexternal force is applied to a tire rubber. As the value of tan δbecomes larger, the energy loss due to a bend of a tire increases and,as a result, the rolling resistance increases.

Specifically, δ (i.e., phase difference) of tan δ can be measured bymoving exciting) the surface of the aforementioned load roll 44alternately in a direction in which the surface of the load roll 44comes closer to the tire 2 and in a direction in which it goes away fromthe tire 2. More specifically, when the surface of the load roll 44 ismoved alternately in these directions, a variation of the load acting onthe tire 2 is observed a little in advance of a variation of the surfaceposition of the load roll 44. The tangent of a phase deviation betweenthese variations calculated by comparing these variations corresponds tothe aforementioned tan δ. In the evaluation device 10 according to theembodiment, the rolling resistance of the tire 2 is evaluated on thebasis of whether a value of tan δ calculated in this manner is largerthan a predetermined threshold value.

In evaluating the rolling resistance of the tire 2 with the evaluationdevice 10, it is necessary to apply exciting force to the tire 2 bymoving the load rolls 44 pressed against the tire 2 toward the tire 2.To move the load rolls 44 alternately in the approaching direction andin the leaving direction, the pressure supplied to the air cylinder 13for driving the load rolls 44 is switched between high pressure and lowpressure. The load rolls 44 apply exciting force to the tire 2 in thismanner, whereby the load acting on the tire 2 is increased anddecreased.

More specifically, in an initial state, the first electromagnetic valve24 and the second electromagnetic valve 25 are off and hence thepressure in the pressure chamber 15 of the air cylinder 13 isatmospheric pressure. In this state, since the springs 12 urge thehousing 30 toward the erected wall 11, the load rolls 44 are separatedfrom the tire 2. Starting from this state, the first electromagneticvalve 24 is switched on while the second electromagnetic valve 25 iskept off, whereby a high pressure is introduced into the pressurechamber 15 and the air cylinder 13 pushes the housing 30 toward the tire2 against the urging forces of the springs 12. As a result, the loadrolls 44 advance and are pressed against the tire 2 so that the loadmeasured by the load cells 38 becomes equal to a prescribed load (seeFIG. 7).

Then the second electromagnetic valve 25 is switched from off to onwhile the first electromagnetic valve 24 is kept on, whereby a lowpressure is introduced into the pressure chamber 15 and the load rolls44 retreat due to reaction forces from the tire 2. That is, the loadrolls 44 retreat in the direction opposite to the pressing directionfrom the state where they were pressed against the tire 2, whereby theload is reduced.

Subsequently, the second electromagnetic valve 25 is switched on and offat a prescribed frequency while the first electromagnetic valve 24 iskept on, whereby the load rolls 44 apply a variable load to the tire 2while the load rolls 44 are kept in contact with the tire 2.

In this case, a variation of the surface position of the load roll 44 ismeasured by the position sensor 37 and a variation of the load ismeasured by the load cells 38. Thus, the temporal variation of theposition of the load roll 44 and the variation of the load are measured,and then curves as shown in FIG. 9 are obtained by extracting onlyexcitation frequency components with a filter or the like and plottingthem.

As shown in FIG. 9, because of the attenuation property of the tirerubber, the variation curve of the load is recorded so as to lead, by aphase difference δ, the variation curve of the roll displacement in thedirection of the pressing force acting on the tire 2. Thus, the phasedifference calculation unit 48 calculates a phase difference δ in thehorizontal direction between the variation curve of the rolldisplacement and the variation curve of the load. Typically, in manycases, a phase difference between these signal waveforms is calculatedby determining a transfer function by an FFT analysis.

A value of tan δ is calculated from the phase difference 3 thuscalculated, and a rolling resistance of the tire 2 is evaluated on thebasis of whether the calculated tan δ exceeds a predetermined thresholdvalue. More specifically, first, a phase difference δ is measured for areference tire that has no abnormality in properties. Subsequently, aphase difference δ of a tire as an evaluation target is measured. If thedifference from the value of the phase difference δ of the referencetire is larger than an allowable range, in other words, if the phasedifference δ is larger than the prescribed threshold value, it can bejudged that the rolling resistance of the tire is larger than a standardvalue. Thus, if the phase difference δ is larger than the prescribedthreshold value, the rolling resistance evaluation unit 49 judges thatthe tested tire is abnormal in rolling resistance and eliminates thetested tire if necessary.

If a calculated tan δ value is smaller than or equal to thepredetermined threshold value (in other words, tan δ is within aprescribed range determined from the value of the phase difference δ ofthe reference tire), the rolling resistance evaluation unit 49 judgesthat the tire as an evaluation target has a normal rolling resistanceand the tire is handled as one that satisfies product standards.

After completion of the rolling resistance evaluation test, the firstelectromagnetic valve 24 and the second electromagnetic valve 25 areswitched from on to off to finish supply of pressure to the pressurechamber 15. As a result, the pressure in the pressure chamber 15 becomesatmospheric pressure and the springs 12 move the housing 30 toward theerected wall 11 while urging the housing 30. The load rolls 44 leave thetire 2.

The use of the aforementioned evaluation device 10 makes it possible todetermine tan δ, which is highly correlated with a rolling resistance ofa tire, and to evaluate the rolling resistance of the tire easily on thebasis of the determined tan δ. This makes it possible to sort out tiresthat are abnormal in rolling resistance accurately in short time andhence to inspect rolling resistance values of all of numerous tireproducts manufactured.

[Features of Device for Evaluating Tire Rolling Resistance According toEmbodiment]

The evaluation device 10 according to the embodiment has the followingfeatures.

In the evaluation device 10 according to the embodiment, because of theuse of the load rolls 44 that are smaller in diameter than the tire 2,the mass of the load rolls 44 can be reduced to a large extent. Thismakes it possible to decrease the capacity of the motive power sourcefor obtaining a prescribed excitation amplitude for the load rolls 44and to reduce vibration and fatigue damage of the entire device and themoving mechanism. By disposing the two or more load rolls 44 side byside, the contact state of the tire 2 can be made closer to its actualground contact state and the curvature of deformation of the tire 2 canbe made smaller.

In the evaluation device 10 according to the embodiment, since the loadrolls 44 are disposed separately from each tire testing machine fortesting properties or performance of a tire such as a tire uniformitytester, a tire balancer, or a running test machine, a device forevaluating tire rolling resistance 10 having the same specification canbe installed easily in various testing machines of differentmanufacturers or different models without modifying existing testmachines or with subjecting them to only simple modifications.

In the evaluation device 10 according to the embodiment, since the loadrolls 44 are disposed separately from the running drum 4 of the tireuniformity tester 1, which is a particular kind among tire testingmachines, a device for evaluating tire rolling resistance 10 can beinstalled without modifying an existing tire uniformity tester 1 or withsubjecting an existing tire uniformity tester 1 to only simplemodifications.

In the evaluation device 10 according to the embodiment, as the radialdimension of the two load rolls 44 becomes larger, the distance betweenthe centers of the two load rolls 44 increases and the contact states ofthe load rolls 44 and the tire 2 become much different from an actualground contact state of the tire. In view of this, by locating thecenters C2 and C3 of the load rolls 44 between the two straight lines L7that are tangential to the tire 2 and pass through the center C4 of theimaginary circle 46 that is tangential to the tire 2 and has the samediameter as the outer diameter of the tire 2, the distance between thecenters of the two load rolls 44 can be made small and the contact stateof the tire 2 can be made closer to its actual ground contact state.

In the evaluation device 10 according to the embodiment, in the case themoving mechanism has the air cylinder 13, the air cylinder 13 isprovided as an inexpensive and simple motive power source. Switching thepressure supplied to the air cylinder 13 between a high pressure and alow pressure allows the load rolls 44 to apply stable exciting force tothe tire 2.

The embodiment of the invention is described above with reference to thedrawings, it should be noted that specific configurations are possiblethat are different from the embodiment. The scope of the invention isdetermined by not only the aforementioned embodiment but also the claimsand includes all modifications made within the confines of the claimsand their equivalents.

Although in the embodiment the evaluation device 10 is attached to thetire uniformity tester 1, the same advantages can be obtained when it isattached to any of various tire testing machines for testing propertiesor performance of a tire such as a tire balancer and a running testmachine.

Although in the embodiment the two load rolls 44 are used, there is noparticular limitation on the number of load rolls 44 except that plural(e.g., three) load rolls 44 should be used. Furthermore, there is noparticular limitation on the specific value of the outer diameter of theload rolls 44 except that their outer diameter should be smaller thanthe outer diameter of the tire 2.

Although in the embodiment the two load rolls 44 have the same outerdiameter, plural load rolls having different outer diameters may beused. Furthermore, in the embodiment, the distance L3 between the centerC2 of the one load roll 44A and the center C1 of the tire 2 is equal tothe distance L4 between the center C3 of the other load roll 44B and thecenter C1 of the tire 2. However, the invention is not limited thiscase. The distances L3 and L4 may be different from each other.

Although in the embodiment the air cylinder 13 is used to apply excitingforce to the load rolls 44 and the tire 2, the invention is not limitedthis case. The same advantages can be obtained by, for example, acombination of a hydraulic cylinder and a hydraulic circuit or acombination of a ball screw and a servo motor. An example in which aball screw and a servo motor are used is described later as a secondmodification.

The evaluation device 10 according to the invention can be applied tovarious tires 2 that are different from each other in outer diameter.FIG. 10 is a side view of the evaluation device 10 applied to a tire 2that is smaller in outer diameter than the tire 2 used in theembodiment. In this case, the load rolls 44 are pressed against the tire2 by elongating the stroke of the air cylinder 13 by moving the piston14 of the air cylinder 13 toward the side of the tire 2. FIG. 11 is aside view of the evaluation device 10 applied to a tire 2 that is largerin outer diameter than the tire 2 used in FIG. 10. In this case, theload rolls 44 are pressed against the tire 2 by shortening the stroke ofthe air cylinder 13 by moving the piston 14 of the air cylinder 13toward the side of the fixing member 6.

Modification 1

In the aforementioned embodiment, the load cells are used as the loadsensors for measuring a load acting on a tire 2 when the load rolls 44are pressed against the tread surface of the tire 2. In contrast, in anevaluation device 10 according to a first modification shown in FIG, 12and FIG. 13, stress gauges 51 are used as the load sensors in place ofthe load cells. Since the other parts of the configuration of theevaluation device 10 are the same as the aforementioned embodiment, thesame reference symbols are assigned to the same elements as employed inthe embodiment and the descriptions thereof are omitted.

In the first modification, top and bottom end portions of each rollshaft 41 are formed with cutouts 52 (52 a and 52 b). One cutout 52 aformed in one of the top and bottom end portions is opposed to the backwall 34 of the housing 30 and the other cutout 52 b is formed on theopposite side of the center axis of the roll shaft 41 to the one cutout52 a. A load applied to the tire can be measured by attaching stressgauges 51 to the respective cutouts 52.

Modification 2

In the aforementioned embodiment, the evaluation device 10 is fixeddirectly to the fixing member 6. However, the invention is not limitedto this case. The evaluation device 10 may be installed on the fixingmember 6 so as to be movable with respect to a tire 2. Morespecifically, as shown in FIG. 14 and FIG. 15, the evaluation device 10is installed, via linear guides 27, on a base portion 56 that is fixedto a fixing member 6. The evaluation device 10 thus installed is movedrelative to the tire 2 by a ball screw 58 that is driven by a servomotor 57 that is fixed to the fixing member 6. The evaluation device 10having this configuration can be applied to various tires 2 havingdifferent outer diameters.

The present application is based on Japanese Patent Application No.2016-183371 filed on Sep. 20, 2016, the disclosure of which isincorporated herein by reference.

DESCRIPTION OF SYMBOLS

-   1: Tire uniformity tester (tire testing machine)-   2: Tire-   4: Running drum-   10: Device for evaluating tire rolling resistance-   12: Spring (moving mechanism)-   13: Air cylinder (moving mechanism)-   37: Position sensor-   38: Load cell (load sensor)-   44, 44A, 44B: Load roll-   46: Imaginary circle-   48: Phase difference calculation unit-   49: Rolling resistance evaluation unit-   51: Stress gauge (load sensor)

1. A device for evaluating tire rolling resistance, the devicecomprising: load rolls having surfaces that simulate a road surface onwhich a tire is to travel; a moving mechanism configured to move theload rolls alternately in an approaching direction in which the loadrolls come closer to the tire and in a leaving direction in which theload rolls go away from the tire; a load sensor configured to detect aload acting on the tire in a state where the surface of the load rollsare in contact with the tire; a position sensor configured to detect aposition of the load roll in a direction along the approaching directionand the leaving direction; a phase difference calculation unitconfigured to control the moving mechanism so that the load acting onthe tire is varied and calculate a phase difference between a variationof the load and a variation of the position of the load roll on thebasis of signals from the load sensor and the position sensor; and arolling resistance evaluation unit configured to evaluate a rollingresistance of the tire as an evaluation target by comparing the phasedifference calculated for the tire as the evaluation target by the phasedifference calculation unit with a phase difference calculated for areference tire by the phase difference calculation unit, wherein theload rolls are two or more load rolls disposed side by side and aresmaller in diameter than the tire.
 2. The device for evaluating tirerolling resistance according to claim 1, wherein the load rolls aredisposed separately from a tire testing machine for testing the tire. 3.The device for evaluating tire rolling resistance according to claim 2,wherein the load rolls are disposed separately from a running drum ofthe tire testing machine.
 4. The device for evaluating tire rollingresistance according to claim 1, wherein the load rolls are two loadrolls, and wherein the centers of the respective load rolls are locatedbetween two straight lines that are tangential to the tire and passthrough the center of an imaginary circle that is tangential to the tireand has the same diameter as the outer diameter of the tire.
 5. Thedevice for evaluating tire rolling resistance according to claim 3,wherein the load rolls are two load rolls, and wherein the centers ofthe respective load rolls are located between two straight lines thatare tangential to the tire and pass through the center of an imaginarycircle that is tangential to the tire and has the same diameter as theouter diameter of the tire.
 6. The device for evaluating tire rollingresistance according to claim 1, wherein the moving mechanism has an aircylinder, and wherein the load rolls are configured to apply excitingforce to the tire by switching the pressure supplied to the air cylinderbetween high pressure and low pressure.
 7. The device for evaluatingtire rolling resistance according to claim 2, wherein the movingmechanism has an air cylinder, and wherein the load rolls are configuredto apply exciting force to the tire by switching the pressure suppliedto the air cylinder between high pressure and low pressure.
 8. Thedevice for evaluating tire rolling resistance according to claim 3,wherein the moving mechanism has an air cylinder, and wherein the loadrolls are configured to apply exciting force to the tire by switchingthe pressure supplied to the air cylinder between high pressure and lowpressure.
 9. The device for evaluating tire rolling resistance accordingto claim 4, wherein the moving mechanism has an air cylinder, andwherein the load rolls are configured to apply exciting force to thetire by switching the pressure supplied to the air cylinder between highpressure and low pressure.
 10. The device for evaluating tire rollingresistance according to claim 5, wherein the moving mechanism has an aircylinder, and wherein the load rolls are configured to apply excitingforce to the tire by switching the pressure supplied to the air cylinderbetween high pressure and low pressure.